High pressure oxygen valve

ABSTRACT

A high pressure valve for oxygen service comprises a valve body ( 10 ) with a gas passage ( 12 ) and a valve seat ( 18 ) associated with the gas passage ( 12 ). An obturation unit ( 22 ) is movable between a first position, wherein it is spaced from the valve seat ( 18 ), and a second position, wherein it is seated on the valve seat ( 18 ). This obturation unit ( 22 ) has a sealing surface ( 24 ) that is in sealing contact with the seat surface ( 20 ) in said second position of the obturation unit ( 22 ). A metallic sealing element ( 32 ) and a synthetic sealing element ( 34 ) co-operate to form the sealing surface ( 24 ). The metallic sealing element ( 32 ) forms the sealing surface ( 24 ) around said inner border of the seat surface ( 20 ), and the synthetic sealing element ( 34 ) forms the sealing surface ( 24 ) towards the outer border of the seat surface ( 20 ).

CROSS REFERENCE TO RELATED APPLICATION

The present application is the U.S. national stage application ofInternational Application PCT/EP00/10572, filed Oct. 26, 2000, whichinternational application was published on May 3, 2001 as InternationalPublication WO 01/31239. The International Application claims priorityof Luxembourg Patent Application 90467, filed Oct. 27, 1999.

FIELD OF THE INVENTION

The present invention generally relates to a high pressure valve foroxygen service and more particularly to such a valve with a syntheticsealing element.

BACKGROUND OF THE INVENTION

High pressure valves with synthetic sealing elements, in particularplastomers as e.g. polyamides (Nylon®)), polychlorotrifluoroethylenes(KEL-F®), polyurethanes or polyetheretherketones, are well known in theart. They provide a far better sealing result than high pressure valveswith metallic sealing elements. However, when valves are to be used inoxygen circuits with high flow rates and high gas pressures (as e.g. inoxygen cylinder filling stations), synthetic sealing elements have to beavoided. The reason for avoiding synthetic materials in valves for suchapplications is the risk of ignition due to adiabatic compressionshocks. Rapid and important flow rate increases in a high pressureoxygen circuit—which may e.g. be due to the quick opening of a valve inthe circuit—result in an adiabatic compression of the oxygen in the seatarea of the valve, which will be accompanied by an important heatgeneration. Such adiabatic compression shocks can result in temperaturepeaks that do by far exceed the ignition temperature of known syntheticsealing materials. Once ignition of the synthetic sealing element hasstarted in the oxygen flux, it will quickly spread and will in mostcases result in a so called oxygen burnout of the valve. Such an oxygenburnout of the valve does not only destroy the valve, it may also resultin fire and explosions.

The risk of important adiabatic compression shocks in the valve—andconsequently the risk of oxygen burnout of the valve—increases with gaspressure. Therefore, oxygen valves to be used for pressures above 200bars have nowadays exclusively metallic sealing elements. However, highpressure valves with metallic sealing elements provide less good sealingresults than high pressure valves with synthetic sealing elements.

OBJECT OF THE INVENTION

A technical problem underlying the present invention is to provide ahigh pressure valve for oxygen service with a good adiabatic compressionresistance and a good sealing result.

SUMMARY OF THE INVENTION

This problem is solved by a high pressure valve for oxygen service asclaimed in the claims.

A high pressure valve in accordance with the present invention comprisesa valve body with a gas passage and a valve seat associated with thisgas passage. The valve seat has an annular seat surface, extendingbetween an inner and outer border. An obturation unit is movable in thevalve body between a first position, wherein it is spaced from the valveseat, and a second position, wherein it is seated on the valve seat.This obturation unit has a sealing surface that is in sealing contactwith the seat surface in said second position of the obturation unit. Inaccordance with an important aspect of the present invention, the valvecomprises a metallic sealing element and a synthetic sealing elementco-operating to form the sealing surface. The metallic sealing elementforms the sealing surface around the inner border of the seat surface,whereas the synthetic sealing element forms the sealing surface towardsthe outer border of the seat surface. It will be appreciated that themetallic seal is responsible for good test results in adiabaticcompression tests with oxygen, because it forms that part of the sealingsurface that is the most exposed to overheating in case of an adiabaticcompression shock in the valve, in particular if the valve is fullyclosed or only slightly open. The synthetic sealing element forms therest of the sealing surface in a more protected position and isresponsible for good sealing results at high pressures.

The metallic sealing element and the synthetic sealing elementpreferably co-operate to form a flat composite sealing surface. This canbe advantageously achieved by housing the metallic sealing element in anannular groove of the synthetic sealing element. In this case thesynthetic sealing element is advantageously a seal ring with an annulargroove along an inner border. The metallic sealing element could be ametallic disc centred in the synthetic sealing element, but it ispreferably only a thin seal ring housed in an annular groove of thesynthetic sealing element. It is made of a ductile metal that does notreact with oxygen and has a good thermal conductivity. A preferredmaterial is e.g. silver. The synthetic sealing element is preferablymade of a plastomer.

In a preferred embodiment, the obturation unit includes a cylindricalprojection protruding beyond the sealing surface. This cylindricalprojection is slidingly fitted in a cylindrical bore of the gas passage.In the fully closed valve, the small radial play subsisting between thecylindrical walls of the cylindrical projection and the cylindrical boreis axially closed by the metallic sealing element. In case of anadiabatic shock in the fully closed valve, the compression heat will bedissipated in the small radial play subsisting between the cylindricalwalls of the cylindrical projection and the cylindrical bore. As thisspace is axially closed by the metallic sealing element, there is nocontact between the hot oxygen and the synthetic sealing element.

The aforementioned cylindrical projection advantageously includes afrontal orifice in its front surface, at least one lateral orifice inits cylindrical lateral surface and an internal gas passage providing aconnection between the frontal orifice and the at least one lateralorifice. Thus the cylindrical projection is capable of radiallydeviating the axial gas stream in the opened valve, so that no gasstream impinges on the sealing surface. A further advantage of thisembodiment is that the flow rate changes more progressively when thevalve is actuated. This helps to prevent pressure shocks in the circuit.

In a preferred embodiment the seat has the form of a cylindrical ringprotruding in a seat chamber of the valve body. The obturation unit thenhas an annular groove wherein the sealing surface forms an annularbottom area. The cylindrical seat ring is received in the annular groovewhen the obturation unit is brought in its second position. It will beappreciated that the ring and the groove then co-operate to form a sortof labyrinth passage, which reduces gas flow when the valve is onlyslightly opened.

In a preferred embodiment the obturation unit includes an outer bodywith a frontal cylindrical cavity therein and a central cylindrical bodyaxially screwed into the outer body, so as to define an annular groovein the frontal cylindrical cavity. This central body has a shoulderbearing on the metallic sealing element, which is housed in an annulargroove of the synthetic sealing element, so that the central body fixesthe metallic and the synthetic sealing elements in the annular groove.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1: is a sectional view showing in detail a valve and an obturationunit of a valve in accordance with the invention, wherein the obturationunit is spaced from the valve seat;

FIG. 2: is a sectional view as FIG. 1, wherein the obturation unit isseated on the valve seat.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIGS. 1 and 2 show in detail a valve seat and an obturation unit of acorner stop valve, which is conceived for oxygen service at gaspressures above 300 bar. Such a valve is e.g. advantageously used as astop valve in oxygen cylinder filling stations.

The valve shown in FIGS. 1 and 2 comprises a valve body 10 with an inletgas passage 12 and an outlet gas passage 14, which open in a seatchamber 16 at right angles to each other. A seat 18, which has the formof a cylindrical ring, protrudes in the valve chamber 16, wherein theinlet gas passage 12 passes axially through the ring shaped seat 18.Reference number 19 identifies the central axis of the ring shaped seat18. A flat annular seat surface 20 is defined by the frontal top surfaceof the ring shaped seat 18.

Reference number 22 identifies an obturation unit associated with theseat 18. This obturation unit 22 is connected to an actuating stem 23,which is connected itself to an actuating device (not shown). The latterenables to move the obturation unit 22 in the seat chamber 16 along theaxis 19 between a first position (shown in FIG. 1), wherein theobturation unit 22 is spaced from the valve seat 18, so that the valveis fully open, and a second position (shown in FIG. 2), wherein theobturation unit 22 is seated on the valve seat 18, so that the valve isfully closed. In the closed position of the valve, i.e. when theobturation unit 22 is in its second position, a sealing surface 24 ofthis obturation unit 22 is pressed against the seat surface 20.

The obturation unit 22 comprises an outer body 26, with a frontalcylindrical cavity therein, and a central cylindrical body 28 axiallyscrewed into the outer body 26, so as to define an annular groove 30 inthe frontal cylindrical cavity. When the obturation unit 22 is in itssecond position shown in FIG. 2, the ring shaped seat 18 is receivedwithin the annular groove 30, wherein the sealing surface 24, which ispressed against the seat surface 20, forms the annular bottom area ofthe annular groove 30.

In accordance with an important aspect of the present invention, thesealing surface 24 is a composite sealing surface, formed byco-operation of a metallic sealing element 32 and a synthetic sealingelement 34. The metallic sealing element 32 forms the sealing surface 24which is in direct contact with the seat surface 18 around the innerborder of the annular seat surface 18. The synthetic sealing element 34forms the rest of the sealing surface 24 towards the outer border of theseat surface 20.

The synthetic sealing element 34 is preferably a seal ring made of aplastomeric material (as e.g. polyamides (Nylon®),polychlorotrifluoroethylenes (KEL-F®), polyurethanes or polyethers).Preferred plastomeric materials are e.g. polyetheretherketones (PEEK) orpolyethersulphones. As seen on FIGS. 1 and 2, the seal ring 34 has asubstantially rectangular cross-section, wherein its outer diametercorresponds to the inner diameter of the frontal cavity in the outerbody 26. It should be noted that the two rear edges and the outerfrontal edge of the seal ring 34 are chamfered, whereas the innerfrontal edge is replaced by a groove. In this groove is housed themetallic sealing element 32, which has the form of a thin ring. Thisthin ring is preferably made of silver, which is a ductile metal thatdoes not react with oxygen and has moreover a good thermal conductivity.Other possible materials are e.g. gold and platinum, but these materialsare of course much more expensive than silver. A shoulder 36 on thecentral cylindrical body 28 fixes the synthetic seal ring 34 and themetallic ring 32 in the annular groove 30, in which the two ductile sealrings 28, 32 are embedded, with a minimum radial play with regard to thetwo cylindrical walls of the groove. It will be noted that the shoulder36 bears on the metallic ring 32, but that the latter radially projectsbeyond the shoulder to the inner annular segment of the sealing surface24 in the annular groove 30.

The central cylindrical body 28 includes a cylindrical projection 38protruding beyond the sealing surface 24 and the front surface 40 of theouter body 26. This cylindrical projection 38 is slidingly fitted in acylindrical bore 42 at the outlet of the inlet gas passage 12 in theseat chamber 16. It has four lateral orifices 44 in its cylindricallateral surface. These lateral orifices 44 open into a central blindhole 46 that forms a frontal orifice 48 in the front surface of thecylindrical projection 38. A cylindrical base 50 axially separates thelateral orifices 44 from the sealing surface 24.

When the obturation unit 22 is in its sealing position shown in FIG. 2,the lateral orifices 44 are located well inside the cylindrical bore 42.The small radial play subsisting between the cylindrical walls of thebase 50 and the bore 42 is sealed at the inner border of the seatsurface 20 by the metallic seal ring 32. It follows that in this closedposition of the valve, the synthetic sealing element 34 is wellprotected against direct contact with the gas and therefore againstignition in case of an adiabatic compression shock in the closed valve.Hot oxygen entering in the radial play subsisting between thecylindrical walls of the base 50 and the bore 42 is stopped by themetallic seal ring 32 and cannot come into contact with the syntheticsealing element 34.

As soon as the obturation unit 22 is slightly lifted from its seat 18,an annular gas stream establishes in the small radial play subsistingbetween the cylindrical walls of the base 50 and the bore 42. At theoutlet of the cylindrical bore 42, the annular gas stream, which isstill co-axial with the axis 19, impinges on the metallic seal ring 32.The latter deviates the gas stream in the small gap separating the seatsurface 20 and the sealing surface 24. At the outer border of the seat18, the gas stream is a second time deviated to flow through the annulargap between the outer cylindrical surface of the seat 18 and thecylindrical surface of the outer body 26 defining the outer wall of thegroove 30. Thereafter the gas stream enters the seat chamber 16 andleaves the valve through the outlet gas passage 14. It will beappreciated that the region of the sealing surface 24, which is the mostexposed to direct contact with a hot oxygen stream, is the section thathas to radially deviate the annular gas stream. In accordance with theinvention this section of the sealing surface is formed by the metallicseal ring 32. It will further be appreciated that the high flowresistance of the labyrinth type flow path limits gas flow andconsequently—in case of an adiabatic compression shock in the valve—heatflux through the gap separating the seat surface 20 and the sealingsurface 24. It follows that the synthetic seal ring 34 will be exposedto relatively low temperatures in case of an adiabatic compression shockin the slightly opened valve.

If the obturation unit 22 is further lifted from its seat 18, thelateral orifices 44 progressively open into the seat chamber 16. Itfollows that a more and more important gas stream flows through theblind bore 46 and the lateral orifices 44 directly into the seat chamber16. As this gas stream is radially deviated in the cylindricalprojection 38, it does not impinge on the sealing surface 24.Consequently, if an adiabatic compression shock occurs in the openedvalve, most of the compression heat will be dissipated in the solidcylindrical projection 38, without any major effect on the syntheticsealing ring 34.

In FIG. 1 the valve is shown in its fully opened position. It will benoted that the lateral orifices 44 are now fully located in the seatchamber 16. A cylindrical foot 52 of the cylindrical projection 38closes the cylindrical bore 42 and prevents an axial gas stream fromimpinging on the sealing surface 24.

In conclusion, the present invention provides a high pressure oxygenvalve with a synthetic sealing element that nevertheless has good testresults in adiabatic compression tests with oxygen at pressures above300 bar.

1. A high pressure gas valve for oxygen service, comprising: a valvebody with a gas inlet passage; a valve seat associated with said gasinlet passage, said valve seat having an annular seat surface, saidannular seat surface extending between an inner and outer border; anobturation unit movable in said valve body between a first position,wherein it is spaced from said valve seat, and a second position,wherein it is seated on said valve seat, said obturation unit having asealing surface that is in sealing contact with said seat surface insaid second position of said obturation unit; and a metallic sealingelement and a synthetic sealing element co-operating to form saidsealing surface, wherein said metallic sealing element forms the sealingsurface around said inner border of said seat surface, and saidsynthetic sealing element forms said sealing surface towards said outerborder of said seat surface; wherein said metallic sealing element ishoused in an annular groove of said synthetic sealing element, so as toco-operate with said synthetic sealing element to form a flat compositesealing surface.
 2. The high pressure gas valve according to claim 1,wherein said synthetic sealing element is a seal ring with an annulargroove along an inner border.
 3. The high pressure gas valve accordingto claim 2, wherein said metallic sealing element is a thin seal ringhoused in said annular groove.
 4. The high pressure gas valve accordingto claim 3, wherein said metallic sealing element is made of a softmetal.
 5. The high pressure gas valve according to claim 4, wherein saidmetallic sealing element is made of silver.
 6. The high pressure gasvalve according to claim 3, wherein said synthetic sealing element ismade of a plastomer.
 7. The high pressure gas valve according to claim1, wherein said obturation unit includes a cylindrical projectionprotruding beyond said sealing surface; and said gas passage includes acylindrical bore in which said cylindrical projection is slidinglyfitted; wherein in the fully closed valve, the small radial playsubsisting between the cylindrical walls of the cylindrical projectionand the cylindrical bore is axially closed by said metallic sealingelement.
 8. The high pressure gas valve according to claim 7, whereinsaid cylindrical projection includes: a frontal orifice in its frontsurface, at least one lateral orifice in its cylindrical lateralsurface, and an internal gas passage providing a connection between saidfrontal orifice and said at least one lateral orifice.
 9. A highpressure gas valve for oxygen service, comprising: a valve body with agas inlet passage and a seat chamber; a valve seat associated with saidgas inlet passage, said valve seat having the form of a cylindrical ringprojecting into said seat chamber and forming therein an annular seatsurface, said annular seat surface radially extending between an innerand outer border; an obturation unit movable in said valve body betweena first position, wherein it is spaced from said valve seat, and asecond position, wherein it is seated on said valve seat, saidobturation unit having an annular groove receiving said cylindrical ringin said second position of said obturation unit and a sealing surfaceforming an annular bottom area in said annular groove, said sealingsurface being in sealing contact with said seat surface in said secondposition of said obturation unit; and a metallic sealing element and asynthetic sealing element co-operating to form said sealing surface,wherein said metallic sealing element forms the sealing surface aroundsaid inner border of said seat surface, and said synthetic sealingelement forms said sealing surface towards said outer border of saidseat surface.
 10. The high pressure gas valve according to claim 9,wherein said obturation unit includes: an outer body with a frontalcylindrical cavity therein; a central cylindrical body axially screwedinto said outer body so as to define said annular groove in said frontalcylindrical cavity; wherein said central body has a shoulder bearing onsaid metallic sealing element, which is housed in an annular groove ofsaid synthetic sealing element, so that said central body fixes saidmetallic and said synthetic sealing elements in said annular groove. 11.The high pressure gas valve according to claim 10, wherein said centralcylindrical body axially protrudes from said frontal cylindrical cavity.12. The high pressure valve according to claim 11, wherein said centralcylindrical body is slidingly fitted in said gas passage of said valveseat.
 13. The high pressure gas valve according to claim 12, whereinsaid central cylindrical body includes: an axial orifice arranged in itsfront surface, lateral orifices arranged in its cylindrical lateralsurface, and internal gas passages providing a connection between saidaxial orifice and said lateral orifices, wherein said lateral orificeslie in said gas passage when said obturation unit is in its secondposition, and above said seat in said valve chamber when said obturationunit is in its first position.
 14. The high pressure gas valve accordingto claim 9, wherein said metallic sealing element is made of a softmetal.
 15. The high pressure gas valve according to claim 14, whereinsaid metallic sealing element is made of silver.
 16. The high pressuregas valve according to claim 9, wherein said metallic sealing elementand said synthetic sealing element co-operate to form a flat compositesealing surface.
 17. The high pressure gas valve according to claim 9,wherein said metallic sealing element is housed in an annular groove ofsaid synthetic sealing element, so as to co-operate with said syntheticsealing element to form a flat composite sealing surface.
 18. The highpressure gas valve according to claim 17, wherein said synthetic sealingelement is a seal ring with an annular groove along an inner border. 19.The high pressure gas valve according to claim 18, wherein said metallicsealing element is a thin seal ring housed in said annular groove. 20.The high pressure gas valve according to claim 19, wherein said metallicsealing element is made of a soft metal.
 21. The high pressure gas valveaccording to claim 20, wherein said metallic sealing element is made ofsilver.
 22. The high pressure gas valve according to claim 21, whereinsaid synthetic sealing element is made of a plastomer.
 23. The highpressure gas valve according to claim 9, wherein said obturation unitincludes a cylindrical projection protruding beyond said sealingsurface; and said gas passage includes a cylindrical bore in which saidcylindrical projection is slidingly fitted; wherein in the fully closedvalve, the small radial play subsisting between the cylindrical walls ofthe cylindrical projection and the cylindrical bore is axially closed bysaid metallic sealing element.
 24. The high pressure gas valve accordingto claim 23, wherein said cylindrical projection includes: a frontalorifice in its front surface, at least one lateral orifice in itscylindrical lateral surface, and an internal gas passage providing aconnection between said frontal orifice and said at least one lateralorifice.
 25. A high pressure gas valve for oxygen service, comprising: avalve body with a gas inlet passage including a cylindrical bore; avalve seat associated with said gas inlet passage, said valve seathaving an annular seat surface, said annular seat surface radiallyextending between an inner and outer border; an obturation unit movablein said valve body between a first position, wherein it is spaced fromsaid valve seat, and a second position, wherein it is seated on saidvalve seat, said obturation unit having a sealing surface that is insealing contact with said seat surface in said second position of saidobturation unit; said obturation unit including a cylindrical projectionprotruding beyond said sealing surface and being fitted with a smallradial play in said cylindrical bore of said valve body so as to delimittherein an annular gas passage; and a metallic sealing element and asynthetic sealing element co-operating to form said sealing surface,wherein said synthetic sealing element forms said sealing surfacetowards said outer border of said seat surface and said metallic sealingelement forms said sealing surface around said inner border of said seatsurface and axially closes said annular gas passage in said secondposition of said obturation unit, wherein said metallic sealing elementis housed in an annular groove of said synthetic sealing element, so asto co-operate with said synthetic sealing element to form a flatcomposite sealing surface.
 26. The high pressure gas valve according toclaim 25, wherein said synthetic sealing element is a seal ring with anannular groove along an inner border.
 27. The high pressure gas valveaccording to claim 26, wherein said metallic sealing element is a thinseal ring housed in said annular groove.
 28. A high pressure gas valvefor oxygen service, comprising: a valve body with a gas inlet passage; avalve seat associated with said gas inlet passage, said valve seathaving an annular seat surface, said annular seat surface extendingbetween an inner and outer border; an obturation unit movable in saidvalve body between a first position, wherein it is spaced from saidvalve seat, and a second position, wherein it is seated on said valveseat, said obturation unit having a sealing surface that is in sealingcontact with said seat surface in said second position of saidobturation unit; and a sealing element made of a soft metal and asynthetic sealing element cooperating to form said sealing surface,wherein said sealing element made of a soft metal forms the sealingsurface around said inner border of said seat surface, and saidsynthetic sealing element forms said sealing surface towards said outerborder of said seat surface, wherein said sealing element made of a softmetal is housed in an annular groove of said synthetic sealing element,so as to co-operate with said synthetic sealing element to form a flatcomposite sealing surface.
 29. The high pressure gas valve according toclaim 28, wherein said sealing element made of a soft metal is a thinsilver seal ring housed in said annular groove.
 30. A high pressure gasvalve for oxygen service, comprising: a valve body with a gas inletpassage; a valve seat associated with said gas inlet passage, said valveseat having an annular seat surface, said annular seat surface extendingbetween an inner and outer border; an obturation unit movable in saidvalve body between a first position, wherein it is spaced from saidvalve seat, and a second position, wherein it is seated on said valveseat, said obturation unit having a sealing surface that is in sealingcontact with said seat surface in said second position of saidobturation unit; and a sealing element made of a soft metal and asynthetic sealing element cooperating to form said sealing surface,wherein said sealing element made of a soft metal forms the sealingsurface around said inner border of said seat surface, and saidsynthetic sealing element forms said sealing surface towards said outerborder of said seat surface, wherein said synthetic sealing element is aseal ring with an annular groove along an inner border.